linux-kernel - RE: [RFC][PATCH v0] x86/hyperv: Reserve 3 interrupt vectors used exclusively by mshv

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID:
 <SN6PR02MB41575124C6D2CD7492899991D4BBA@SN6PR02MB4157.namprd02.prod.outlook.com>
Date: Fri, 2 Jan 2026 16:02:52 +0000
From: Michael Kelley <mhklinux@...look.com>
To: Vitaly Kuznetsov <vkuznets@...hat.com>, Mukesh Rathor
	<mrathor@...ux.microsoft.com>, "linux-hyperv@...r.kernel.org"
	<linux-hyperv@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
CC: "kys@...rosoft.com" <kys@...rosoft.com>, "haiyangz@...rosoft.com"
	<haiyangz@...rosoft.com>, "wei.liu@...nel.org" <wei.liu@...nel.org>,
	"decui@...rosoft.com" <decui@...rosoft.com>, "longli@...rosoft.com"
	<longli@...rosoft.com>, "tglx@...utronix.de" <tglx@...utronix.de>,
	"mingo@...hat.com" <mingo@...hat.com>, "bp@...en8.de" <bp@...en8.de>,
	"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>, "x86@...nel.org"
	<x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>
Subject: RE: [RFC][PATCH v0] x86/hyperv: Reserve 3 interrupt vectors used
 exclusively by mshv

From: Vitaly Kuznetsov <vkuznets@...hat.com> Sent: Friday, January 2, 2026 7:55 AM
> 
> Mukesh Rathor <mrathor@...ux.microsoft.com> writes:
> 
> > MSVC compiler used to compile the Microsoft Hyper-V hypervisor currently,
> > has an assert intrinsic that uses interrupt vector 0x29 to create an
> > exception. This will cause hypervisor to then crash and collect core. As
> > such, if this interrupt number is assigned to a device by linux and the
> > device generates it, hypervisor will crash. There are two other such
> > vectors hard coded in the hypervisor, 0x2C and 0x2D.
> >
> > Fortunately, the three vectors are part of the kernel driver space, and
> > that makes it feasible to reserve them early so they are not assigned
> > later.
> >
> > Signed-off-by: Mukesh Rathor <mrathor@...ux.microsoft.com>
> > ---
> >  arch/x86/kernel/cpu/mshyperv.c | 22 ++++++++++++++++++++++
> >  1 file changed, 22 insertions(+)
> >
> > diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> > index 579fb2c64cfd..19d41f7434df 100644
> > --- a/arch/x86/kernel/cpu/mshyperv.c
> > +++ b/arch/x86/kernel/cpu/mshyperv.c
> > @@ -478,6 +478,25 @@ int hv_get_hypervisor_version(union hv_hypervisor_version_info *info)
> >  }
> >  EXPORT_SYMBOL_GPL(hv_get_hypervisor_version);
> >
> > +/*
> > + * Reserve vectors hard coded in the hypervisor. If used outside, the hypervisor
> > + * will crash or hang or break into debugger.
> > + */
> > +static void hv_reserve_irq_vectors(void)
> > +{
> > +	#define HYPERV_DBG_FASTFAIL_VECTOR	0x29
> > +	#define HYPERV_DBG_ASSERT_VECTOR	0x2C
> > +	#define HYPERV_DBG_SERVICE_VECTOR	0x2D
> > +
> > +	if (test_and_set_bit(HYPERV_DBG_ASSERT_VECTOR, system_vectors) ||
> > +	    test_and_set_bit(HYPERV_DBG_SERVICE_VECTOR, system_vectors) ||
> > +	    test_and_set_bit(HYPERV_DBG_FASTFAIL_VECTOR, system_vectors))
> > +		BUG();
> 
> Would it be less hackish to use sysvec_install() with a dummy handler
> for all three vectors instead?

It would be, but unfortunately, it doesn't work. sysvec_install() requires
that the vector be >= FIRST_SYSTEM_VECTOR, and these vectors are not.

Michael

> 
> > +
> > +	pr_info("Hyper-V:reserve vectors: %d %d %d\n", HYPERV_DBG_ASSERT_VECTOR,
> > +		HYPERV_DBG_SERVICE_VECTOR, HYPERV_DBG_FASTFAIL_VECTOR);
> > +}
> > +
> >  static void __init ms_hyperv_init_platform(void)
> >  {
> >  	int hv_max_functions_eax, eax;
> > @@ -510,6 +529,9 @@ static void __init ms_hyperv_init_platform(void)
> >
> >  	hv_identify_partition_type();
> >
> > +	if (hv_root_partition())
> > +		hv_reserve_irq_vectors();
> > +
> >  	if (cc_platform_has(CC_ATTR_SNP_SECURE_AVIC))
> >  		ms_hyperv.hints |= HV_DEPRECATING_AEOI_RECOMMENDED;
> 
> --
> Vitaly
>